Modules are being developed wherein a plurality of circuit boards mounting circuits consisting of electronic and electric components, etc. are stacked with a predetermined distance between the circuit boards. In this type of module, the circuit boards are held parallel to one another by a holding member. Compared to the case where a plurality of circuit boards is disposed on the same plane, stacking the plurality of circuit boards by means of the holding member allows this module to save space. This type of module is utilized while housed within a housing or the like. For example, this type of module is utilized in an information processing device mounted in a vehicle, etc.
It is desirable that a large amount of information is transmitted accurately between the stacked circuit boards. Japanese Utility Model Application Laid-Open Publication No. 1993-77954 teaches a module in which a light receiving element and a light emitting element are utilized to transmit information between circuit boards. In this module, the light emitting element is disposed on one circuit board and the light receiving element is disposed on an other circuit board. From a plan view, the light emitting element and the light receiving element are disposed so as to overlap. In the technique set forth in Japanese Utility Model Application Laid-Open Publication No. 1993-77954, an optical signal emitted from the light emitting element is received by the light receiving element, thereby realizing optical communication between the circuit boards. In the module of Japanese Utility Model Application Laid-Open Publication No. 1993-77954, the optical signal travels through a space between the circuit boards.